The Influence of Vegetation on Methane Ebullition in a Temperate Wetland

Abstract:

Methane (CH₄) is a potent greenhouse gas, with wetlands being the main natural source of CH₄ to the atmosphere. Ebullition, or bubbling, is one pathway of CH₄ emission to the atmosphere from wetland ecosystems. Rates of ebullition vary spatially and temporally and can be impacted by vegetation type, peat density, temperature and pressure. We present three years of ebullition measurements from Sallie’s Fen, a temperate peatland located in Barrington, NH. We observed the continuous and episodic nature of ebullition and how it varied with species composition, specifically sedge dominated and shrub dominated areas, using six acoustic and manual sensors. These sensors recorded continuously from June through October in each year (2011-2013). From these sensors, manual collections of accumulated gas were sampled to measure both the volume of gas and concentration of CH₄. To identify differences in ebullition rates due to varying species composition, we installed six additional sensors in June 2013. Measured ebullitive fluxes ranged from 0 to 345 mg/m²/day. Manual measurements in sedge dominated sites had an average flux of 40.8 mg/m²/day for the three year data set compared to an average flux rate of 31.7 mg/m²/day for the shrub dominated sites. Acoustic data shows relationships between water table height and changes in other environmental variables. A subsample of the manual bubble collections at each sensor was also analyzed for ¹³C-CH₄ in order to understand the dominant methanogenic pathway and how this varies with species composition and season.